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Donor milk nutrition for the preterm infant: Current standards, uses, and transitions
Key points
- 1.
Pasteurized donor human milk is the preferred alternative feeding source when maternal milk is not available for preterm and low-birth-weight infants.
- 2.
Holder pasteurization, freezing, and handling of donor human milk leads to decreased macronutrient content by reducing fat and protein levels. It also decreases many biologically active components that serve immunologic benefits. Some human milk immunoregulatory bioactives, such as human milk oligosaccharides, are preserved throughout these processes.
- 3.
While studies are limited and results are variable, many researchers have reliably found lower in-hospital growth rates for infants fed predominately donor breast milk, both nonfortified and fortified, compared to infants fed preterm or term formula. These studies have not supported an effect of donor milk versus formula on long-term growth, neurodevelopment, or all-cause mortality.
- 4.
Current randomized trials of donor human milk versus formula were not designed with necrotizing enterocolitis as the primary outcome; however, meta-analysis of the most current randomized clinical trials supports the use of donor human milk as a supplement to maternal milk for preterm infants, instead of formula, to decrease the risk of necrotizing enterocolitis.
- 5.
Although research supports a potential cost benefit in the use of donor human milk in hospitals for preterm infants, the burden of cost is often cited as a barrier to access. Variable insurance reimbursement policies and limited human milk banks nationwide contribute to shortages in donor human milk. Racial and economic inequities persist regarding access to donor human milk. Healthcare prescribers should work together to improve access for all patients who would benefit, especially those from diverse backgrounds.
- 6.
While many Level III and IV newborn care facilities nationwide have established donor human milk programs, heterogeneity exists among eligibility and weaning criteria. Scientific evidence regarding best practices and timing for transition from donor human milk to formula is lacking. Further studies are warranted to aid in the development and adaptation of standardized donor human milk practice guidelines.
Introduction and historical background
Human milk provides nutritional and immunologic factors for optimal infant growth and development, yet not every mother is able to provide this resource to their infant. When the gold standard of maternal milk (MM) is not available, infant formulas manufactured to approximate the macro- and micronutrients of human milk are available in most countries. Another option is donor human milk (DHM). The World Health Organization (WHO) and the American Academy of Pediatrics (AAP) guidelines recommend DHM rather than formula as the alternative feeding source when MM is not available. , Understanding the production of, options for, and evidence regarding DHM is key to providing this resource in the NICU.
Donation of human milk historically encompasses wet nursing, informal milk sharing, and milk banking. In most contemporary NICUs, DHM is obtained formally from a bank with safety protocols to ensure the milk has no detectable microbes. Milk pasteurization and microbial testing are the primary methods by which a DHM bank achieves this goal. Other methods to improve preservation of the immune activity of milk, such as ultraviolet irradiation or high-pressure processing without high heat, show promising results but are not yet clinically available.
Differences in pasteurization techniques
The mainstay of DHM banking is Holder pasteurization (HoP) , a method in which milk is heated to 62.5°C for 30 minutes. Another common form of pasteurization is vat pasteurization , which is like HoP but differs in that the milk is heated in a large “vat” rather than in individual milk bottles and is heated to 63°C and for longer than 30 minutes. A third form is retort processing , which is a process that includes not only heat but also pressure, resulting in a commercially sterile milk product. Although these processes remove or inactivate pathogens, they also decrease the biologically active components of human milk. Investigation is ongoing to identify the best methods by which to remove infection risk while protecting immune components with processes that can be available in low- and middle-resource countries.
Donor human milk standards
Formal milk banking has developed through regional standards set by organizations such as the Human Milk Banking Association of North America (HMBANA), the European Milk Bank Association, and the Brazilian Network of Human Milk Banks that has now been expanded as the Ibero-American Network of Human Milk Banks. These organizations set standards for safety including inclusion and exclusion of milk donors, milk handling, milk pooling, pasteurization, postpasteurization handling, and evaluation for microbial contamination. From a 2019 international symposium on human milk banking came a call for international guidance to ensure quality, safety, and equity in DHM as donor milk availability expands worldwide.
Current use
Pasteurized DHM is recommended by the WHO and the AAP as the enteral nutrition to give to preterm or low-birth-weight infants when the mother’s own milk is not available. , , A growing number of hospitals also are providing donor milk to all newborns as a method to ensure an exclusive human milk diet during birth hospitalization. , Determining how these clinical guidelines and decisions are supported by evidence is critical to ensuring that this limited resource is available to those infants with the greatest need. Additionally, as the use of donor milk grows, the benefits and potential risks in all populations require investigation.
Evidence-based outcomes related to donor human milk
Reduced risk of necrotizing enterocolitis
Necrotizing enterocolitis (NEC) is a severe gastrointestinal inflammatory disease associated with death, short bowel syndrome (SBS), and later neurodevelopmental delay. For neonates, the risk of developing NEC inversely relates to the degree of prematurity. Cohort studies show an intake of MM is associated with a decreased risk of NEC. Randomized trials have investigated whether DHM as a supplement to MM decreases the risk of NEC. The most recent Cochrane Database of Systematic Reviews meta-analysis of preterm or low-birth-weight infants fed either formula or DHM includes nine studies with a total of 1675 infants. Four of the studies were performed in the 1980s and compared formula with unfortified DHM. Four studies compared formula with fortified DHM, three with a cow’s milk–based human milk fortifier (HMF) and one with a DHM-based HMF. The ninth study included in the meta-analysis compared formula and DHM with a primary outcome of days to reach full feed volume (150 mL/kg/d). The average time to full feeds was 12 days for both groups, and in the 70 infants studied, no NEC was diagnosed. In the meta-analysis of the nine studies, the rate of NEC in infants receiving formula was 6.8% and in infants receiving DHM was 3.6%. The formula-fed group had higher risk of NEC: risk ratio (RR) of 1.87 with a 95% confidence interval (95% CI) of 1.23 to 2.85 and a number needed to treat for an additional harmful outcome of 33, classified as moderate certainty evidence.
When individually evaluating the four contemporary studies of preterm formula compared to fortified DHM, none of the studies were specifically powered to identify a difference in NEC outcomes. Two included NEC in a cumulative outcome measure including infection and mortality, , one was powered for neurodevelopmental outcomes, and the fourth was powered for a difference in parenteral nutrition days. Individually, three of the four study results demonstrated no difference in NEC between formula- and DHM-fed preterm infants. , , Furthermore, in three out of four of these studies, DHM was given as a supplement to MM; therefore these findings are not generalizable to populations of infants receiving DHM as the sole source of breast milk. In a meta-analysis including 955 infants from all four studies, a difference in NEC of 9% in formula-fed infants compared to 5.5% in DHM-fed infants and a RR of 1.64 (95% CI 1.03, 2.61) with formula feeding was observed. In all four of these studies, the definition of NEC is poorly defined. A meta-analysis was published in 2019 that reviewed all randomized trials published from January 1960 to January 2018 that specifically investigated the effect of DHM versus preterm formula on the most severe case of NEC, defined as surgical NEC , and found DHM was not protective against surgical NEC over preterm formula. To summarize, due to several limitations in study design and a paucity of data, the evidence for a protective effect of DHM when supplemented with MM over preterm formula against NEC in preterm infants should be interpreted with caution, particularly in prevention of surgical NEC.
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